Electric discharge lamp circuit



N 1942- v A. F. PRESCOTT 2,300,963

ELECTRIC DISCHARGE LAMP CIRCUIT Filed Jan. 27, 1941 Inventor: Allen FTPrescott,

aien tedi rtecrarc nrs v dhnrst, Ohio, mgnor to Allen B. ott

General Electric M a corporation oi New York pplication My inventionrelates" to circuits for electric discharge lamps such, for example, asfluorescent lamps. such lamps of a well known and commonly used formhave electrodes which are constructed and arranged to be heated bycurrent flow therethrough before the discharge in the lamp is started.Because the lamp has a negativetemperature-resistance coefilcient, itsconnection across a source of current of constant potential is madethrough a suitable current controlling impedance. Where a reactor orchoke coil is used for that purpose, the current taken from the sourcewill lag behind the voltage thereof; similarly, where a capacitor isusedjor that purpose or where the impedance includes both a reactor anda capacitor and the net, reactance is capacitive, the current taken drumthe source will lead the voltage thereof.

With continued use the lamps have been ob served to become somewhatblackened at their ends, sometimes more at one and than at the otherdepending largely upon the character of the starter employed, and it hasbeen noticed that the degree of the blackening is dependent chiefly onthe frequency with which the lamps are started. It has also been noticedthat, as a result of successive startings, lamps on leadingcurrentcircuits develop blackened ends much earlier in their life than lamps onlagging-current circuits. It has been found that the electrodes of lampson leading-current circuits are subjected to greater injury, during thestarting of the lamps, than arethc electrodes of lamps onlagging-current circuits, namely, where capacitors are not used.

It is the object of my invention therefore to provide an improved lampleading-current cire cult with which the above noted objections may 27,1941, Serial No. s'iaoai cl. ire-124) the following description taken inconnection with the accompanying drawing and its scope will be pointedout in the appended claims.

In the single figure of the drawing which is a circuit diagramillustrating my invention I have shown a lamp arrangement comprising twoidentical electricdischarge lamps connected to be operatedsimultaneously from the same supply circuit, one'lamp being operated ona lagging-current circuit, and the other lamp being'operated on aleading-current circuit. The advantages 01! such an arrangement inavoidlnga stroboscopic efiect and in obtaining a high power factor arewell known.

In the drawing, 8 represents an electric discharge lamp or thelow'pressure positive column gaseous discharge type which comprises atransparent tubular envelope having a filling of rare gas, or metalvapor, or both. The metal vapor may, for example, be mercury and if thelamp is of the fluorescent type the inner surface of the envelope may becoated with a suitable phosbe avoided. It is the further object of myinvention to provide an improved lamp circuit in which the current isleading during the normal operation of the lamp but is lagging at thetime reality a lagging-current circuit. After a predetermined timeiollowingthe starting of the lamp, however, the capacitor becomesoperative so that the lamp whichwas started on a circuit having alagging-current operates from then on on a circuit having aleading=cuirent.

My invention will be better understood from until after the lamp hasstarted is rendered inoperative so that the lamp circuit becomes in I'phor which will iluoresce when an electric discharge passes through themercury vapor.

directly heated electrodes of well known form.

wherein' the wire coil serves merely as a heater for the electrode.

The lamp is connected to be supplied from the source 5, which may he'scycle, volt alternating current lighting circuit, through theconnections d and ii. In one or these connections, as d, I have shownthe main control switch 6 and inthe other connection, 5, I have shownthe ballast l 101' the lamp which is represented as a reactor or chokecoil, the reactance of which is such that the current taken by the lampis that for which'the lamp is designed. For starting the lamp a starterof any one of various forms may be employed. In the drawing I haverepresented a starter b of the glow discharge type of the character ofthat disclosed and claimed by the Bench Patent 2,200,443. The starterilluswhich the latter comprises a bimetallic element is but which isadapted to engage it when heated by a glow discharge taklng placebetween the two electrodes. Since the contact of the two electrodesshort circuits the discharge path thereapproximately twice that of thenormal lamp current, flows through the lamp electrodes during thatinterval which is of the proper length to enable them to become heatedtoan electron emitting temperature. By the subsequent separation of thestarter electrodes a voltage impulse is applied to the lamp to cause thedischarge therein to start in the well understood manner.

The lamp l is identical with the lamp I and the starter 8 is identicalwith and iunctions'in the same manner as the starter 8. The lamp l' isconnected with the same supply circuit 3 through the connections 4' and5' it'being noted however that the connection 4'.is' such that thecircuit of lamp I is controlled by the same switch 6 as controls lamp l.The ballast for the lamp l comprises the reactor or choke coil 1' whichmay have substantially the same reactance as the reactor 1 and thecapacitor I! connectedin series with the reactor 1'. Inasmuch as thelamp l is ballasted by inductive reactive means, itis obvious thatcurrent taken by the lamp (lur ing its normal operation will lagbehindthe voltage of the source of-supply. In the case of the ballast for thelamp l' where both inductive and capacitive reactance means areemployed, the capacitor is so constructed that the reacconnected in theconnection 5' of the lamp in,

it it becomes blackened at one or both ends and its electrodes suflergreater injury than do those of lamp I.

To avoid these difliculties and disadvantages, I have provided, means bywhich the efiect of the capacitor in the circuit of lamp l' is notremoved until after the lamp has started. The means which I haveillustrated for accomplishing this purpose is the circuit II whichshunts the capacitor l5 and which is controlled by the switch l8. Whilea switch of any one of various types may be used, the form of switchillustrated is a thermal switch comprising the bimetallic armlll havingthe contact 20 at its free end which is adapted to engage the contact 2|supported on the flexible arm 22. The switch is constructed to benormally closed so as to close the shuntcircuit about the capacitor 15.Arranged in thermal relation with the bimetallic strip is is theresistance heater 23 which is shown series with the ballast. The switchl8, including its heater, is so constructed that to eflfect its openingit requires the heat due not only to the current by which the lampelectrodes are preheated but, in addition, to a certain amount or normalcurrent flow in the lamp circuit after the lamp hasstarted. The timerequired for the switch to open after the lamp normally starts operatingis made sufliciently long to allow the starter to make several attemptsto start the lamp if necessary. Since the shunt circuit 11 is closeduntil after the lamp starts, it will be seen 4 that the lamp I alwaysstarts on a lagging-curtance produced by it exceeds the reactance oi thereactor in series therewith and the net capacitive reactance is of sucha value that'the current taken by the lamp is that for which the lamp isdesigned. Moreover, it will be obvious that since the net reactance incircuit with the lamp l. is capacitive, the current taken by that lampwill lead the voltage of the source of supply. Preferably, the phaseangle between the current taken by lamp I and the current taken by lampI is approximately 90 whereby'the stroboscopic effect of the combinedlight of the two lamps is reduced to a minimum value and the powerfactor of the two lamp circuits together is substantially 100 per cent.w

Where the two lamps employed are identical and the two startersemployedtherewithalso are identical as in the present case, aconditionwhich is highly desirable for manufacturing reaf,

sons, the current which flows through the lamp I is somewhat less thanthe current which flo'ws through the lamp I. This may be accounted forby the fact that the combination of inductive L and capacitive reactancein the circuit-oi lamp I' gives to that circuit, to a certain degree, a

rent circuit just as lamp I does. By the opening of the switch after thelamp has been started, the lamp continues to operate but the lamp cur.-rent becomes leading instead of lagging. Thereafter the normallamp'current produces sufllcient heat to hold the switch open.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, an'electric discharge lamp having spaced electrodesadapted to be initially heated by the flow of current therethrough andhaving means for subsequently starting the discharge in the lamp, meanshaving ballasting impedance for connecting said lamp across a source ofcurrent supply, said impedance including a capacitor having 'a lowresistance shunt circuit thereac'ross, and means responsive to thecurrent .in said connecting means for opening said constant-currentproperty; hence the heating v current for the lamp electrodes during theshort interval that the starter electrodes engage each other does notrise to as-high a value inthat lamp as it does in lamp 1. As'a result ofthe lower value of the heating current applied to' the electrodes oflamp I, the starter associated with that lamp may make one ormoreunsuccessiul attempts to start the lamp before the temperature ofits electrodes has reached the proper value. Thus the lamp l'is not onlyslower than the lamp l incoming into operation but by reason of thegreater number of attempts to start shunt circuit after the lamp hasbeen started. 2. In combination, an electric discharge lamp havingspaced electrodes adapted to be initially heated by the now of currenttherethrough and 'having starting means connected between saidelectrodes for interrupting said current flow after a, predeterminedtime delay, means having ballasting impedance for connecting said lampacross a source of current supply, said impedance including acapacitorliaving 'a low resistance shunt circuit thereacross, and meansresponsive to the current in said connecting means for opening saidshunt circuit aitera predetermined time delay materially longer thansaid first mentioned time delay.

3. In combination, an electric discharge lamp having spaced electrodesadapted to be initially heated by the flow of current therethrough andhaving means for starting the discharge in the lamp,- means forconnecting said lamp across a source of alternating current supply, saidmeans including a reactor and a capacitor, a low resistance circuitbridged across said ca pacitor, and means responsive to the current insaid connecting means for opening said bridge circuit after said lamphas started.

4. In combination, an electric discharge lamp having spaced electrodesadapted to be initially heated by the flow of current therethrough andhaving means for starting the discharge in the lamp, means forconnecting said lamp across a source of alternating current supply, saidmeans including a reactor, a capacitor and a resistance he'ater, a shortcircuit bridged across said capacitor, and a thermal switch respon- 5.In combination, an electric discharge lamp having spaced electrodestherein, means including ballast for the lamp for connecting the lamp tobe supplied from a source of current supply, starting means connected inshunt with the lamp, said electrodes being arranged to become initiallyheated by current flow through said connecting and starting means, saidballast including a capacitor having a short circuit thereacross, andmeans responsive to current .in said connecting means for opening saidshort circuit after a. predetermined time. delay.

ALLEN F. PRESCOTT.

t CERTIFIGAZPE QF CORRECTION. Patent No. 2,500,965, A v Nqveqnber' 5,19l;2. ALLEN F. PRESCOTT;

'It. is hereby certified that ei-m-r appears in .the p'rintedspecification of the above numbered patent requiring rrection asfollows: Page 2 'aec- 0nd column, line 6, 'strike outfnot"; and. thatthe seifi Letters Patent qheuld be read with this con-action thereinthat the same mey cobfo m to the recoi'd of the case inthe Pateht OfficeI signed end s'ealed'thie 22nd day: of December, A. n. 19!;2.

v i 4 Heh ry Van hbsd ale, (Seal) Actixgg Cqnmiseio en of Patents.

